Some heart patients experience episodes of atrial tachyarrhythmia, including atrial fibrillation and/or atrial flutter (AF). AF is recognized as the primary cause of thromboembolic stroke and exacerbation of heart failure. AF causes the highest number of hospitalizations and is associated with a high mortality and impaired quality of life. In addition, atrial tachyarrhythmias beget ventricular tachyarrhythmias in some patients.
For heart patients having a multi-chamber pacemaker, AF episodes present an additional problem, in that the pacemaker may coordinate ventricular pacing with atrial activity. When an AF episode begins, it is undesirable for ventricular pacing to track the atrial rhythm. Accordingly, some pacemakers are equipped with a “mode switching” capability. The principal purpose of such mode switching is to prevent the pacing system from delivering ventricular paces that track high rate atrial activity when the atrium experiences an episode of atrial tachycardia. When the atrial rate is normal, the pacemaker assumes a tracking mode, such as DDD or DDDR, in which ventricular pacing tracks atrial activity. When an AF episode occurs, however, the pacemaker mode switches to a non-tracking pacing mode, such as DDIR, and paces the ventricle independently of atrial activity.
When an AF episode occurs, the pacemaker or another medical device may apply therapy to terminate the AF episode. Therapy may include application of a cardioversion shock or administration of drug. Another therapy for atrial tachycardia is anti-tachycardia pacing (ATP) in which a high frequency burst of stimulation pulses is delivered. ATP is often effective in disrupting an atrial arrhythmia such as AF and terminating the episode. Of course, an AF episode may also terminate spontaneously.
It has been observed that a recurrent AF episode may occur within seconds or minutes after the termination of the first, primary AF episode, and herein such an episode is referred to as an early recurring AF (ERAF) episode. Although an ERAF episode does not always follow the termination of a preceding AF episode, it has been demonstrated clinically that a patient may have an increased risk of a recurrent AF episode for a period of time following a prior AF episode, either an initial or another ERAF episode. This phenomenon has been attributed to the fact that the local refractory period after AF is temporarily shortened, causing the substrate to be vulnerable to premature atrial beats which will re-induce AF. In patients with AF, who have a pacemaker implanted, atrial overdrive pacing may influence mechanisms which are held responsible for the early recurrence of AF and thereby reduce the likelihood of ERAF episodes. Post-Mode Overdrive Pacing (PMOP) refers to the delivery of atrial overdrive pacing after termination of a pacing mode switch following termination of an AF episode, when a sinus rhythm has been restored but the tissue is still vulnerable to ERAF episodes induced, for example, by premature beats.